CANH

CANH, or CAN High, is one of the two conductors that form the Controller Area Network (CAN) bus, the other being CANL (CAN Low). Together, these wires carry differential signaling used by CAN transceivers to convey logical bits. Nodes on a CAN network use a CAN transceiver to drive and monitor the CANH and CANL lines, while the controller manages message framing.

electrically, the bus is terminated by 120-ohm resistors at each end, providing a characteristic load across CANH and CANL. When the bus is idle, biasing circuitry keeps the lines in a recessive state. In classic CAN, recessive means both lines sit near the same voltage (about 2.5 V on each line). Dominant state occurs when a node transmits a bit: CANH rises to roughly 3.5–3.8 V while CANL falls to about 1.5 V, creating a differential voltage of around 2 V. The receivers interpret the polarity of this differential signal to recover the transmitted bit. These voltages can vary with supply voltage, bus length, and transceiver design.

CAN signaling features strong noise immunity due to its differential nature, enabling reliable communication in automotive and industrial environments. Arbitration is performed on the bus: if multiple nodes attempt to send, a dominant bit overrides recessive ones, allowing the highest-priority message to win without data collision. CAN supports multi-node networks and error handling through CRC, acknowledge, and error counters.

CAN is widely used in vehicles and industrial systems. In high-speed CAN (CAN 2.0), the standard supports up to about 1 Mbps. CAN FD extends data phase rates and payloads, while CANH and CANL continue to carry the differential signaling that underpins the protocol’s robustness.